1. Technical Field
The present invention relates to thin-film transistors, electro-optical devices, and electronic apparatuses.
2. Related Art
In recent years, organic thin-film field-effect transistors composed of organic semiconductor materials have been receiving attention as devices that would substitute for thin-film field-effect transistors composed of inorganic materials such as silicon.
The reason for this is as follows: for example, (I) since organic thin-film field-effect transistors can be produced at lower temperatures than those of transistors composed of inorganic semiconductor materials, plastic substrates and films can be used as substrates. This makes it possible to produce flexible, lightweight, and durable thin-film transistors; (II) thin-film transistors can be produced in a short period of time by simple methods, such as application methods and printing, including supplying solutions containing organic materials, thereby achieving significantly low process cost and equipment cost; (III) various organic materials can be used. Thus, material properties and characteristics of thin-film transistors can be easily drastically changed by changing molecular structures; and (IV) combinations of different functions of organic semiconductor materials can achieve functions and characteristics of thin-film transistors, in which the functions and characteristics cannot be achieved by the use of inorganic semiconductor materials.
In the case where organic semiconductor layers are composed of organic semiconductor materials having p-type semiconducting properties, such organic thin-film transistors serve as switching elements in which no current flows between source electrodes and drain electrodes when no voltage is applied to gate electrodes (OFF state) and in which current flows between source electrodes and drain electrodes when a negative voltage is applied to gate electrodes (ON state).
To provide excellent functions as switching elements, it has been required to develop thin-film transistors in which substantially no current flows in an OFF state and a large current flows in an ON state.
Hitherto, achieving substantially no current flow in an OFF state has been relatively easy. However, it has been significantly difficult to produce thin-film transistors that allow a large current to flow in an ON state. In recent years, the problem in the ON state has been overcome as results of research and development of thin-film transistors. JP-A-2005-101555 is an example of related art.
Although thin-film transistors that allow a larger current to flow in an ON state have been able to be produced, a problem of current flow in an OFF state has arisen.